1. Field of the Invention:
The present invention relates generally to a gear pump and motor, and more particularly to an improved gear pump and motor adapted for efficient operation at low speeds and having means for controlling the position of a sealing member relative to the gears within the pump and motor.
2. Description of the Prior Art:
Conventional gear pumps and motors are generally of the pressure balance type which tend to improve the pump and motor efficiency by actuating the seal member to a position adjacent to the engaging area of the meshed gears by utilizing the discharge or supply pressure so as to prevent internal oil leakage from the sealing chamber formed by means of the gears and the seal member. The seal member utilized within the conventional gear pumps and motors is thus urged to perform the sealing function in response to the discharge or supply pressure of the oil, and consequently is always actuated in the biased direction. A common occurrence experienced with various construction and industrial machinery employing such gear pumps and motors of the pressure balance type is the reduction in the pumping efficiency and improper responsiveness of the hydraulic components during low speed operation of the drive source and seizure and wear of the seal and rotary members during high speed operation.
Furthermore, when the gear pump and motor is in the idle condition, wherein work is not provided, or the volume discharge of oil which is supplied is more than the required amount, as the pump hydraulic circuit always maintains a hydraulic resistance of approximately 10-15kg/cm.sup.2, such operation results in the consumption of some required power, and yet the discharged hydraulic oil is merely circulating throughout the pump and oil tank. Such operation, however merely consumes power and further increases the temperature of the oil with the result that such is not desirable for either the pump or the conduits and actuators within the hydraulic circuit for the increase in the oil temperature reduces the viscosity of the oil, and accordingly, such results in the decrease of the sealing effect of the seal members whereupon an increase in the internal oil leakage will occur which in turn causes oil leakage within the circuit conduits and actuators. In order to prevent such disadvantages, it is usually necessary to enlarge the conduits and valves so as to reduce the fluid resistance, however, in order to enlarge the valves and conduits, it sometimes becomes difficult to mount the same upon a vehicle, and in addition, it usually is not economical to do so.
The conventional gear pumps and motors have been generally used heretofore for transmission pumps, brake pumps, steering pumps, actuator pumps, or the like, but with respect to the operation of transmission pumps, brake pumps, and steering pumps, such pumps are required to perform their functions even during the idling operation of the engine which is used as a drive source of the pump. However, as the volume efficiency of the pumps of this type is generally reduced when the rotational speed is decreased, and particularly when the oil temperature is high, the volume efficiency may become 50 percent or less, the idling speed of the engine of the construction machinery being approximately 500 - 600 r.p.m. Under such conditions, even simple operations are difficult to perform often or coordinate.
In order to counteract such disadvantages, the speed of the drive source must be increased, or a pump having a larger volume discharge must be preselected. However, such requirements can be inconvenient, and the power loss noted heretofore is not resolved. If a pump having a sufficient capacity for supplying enough oil even during low speed operation of the engine is adopted, it has been noted that excessive torque is produced, and excessive volume discharge must be released through means of a relief valve during high speed operation thereof which of course is not preferable.